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Randomized Controlled Trial
. 2012;7(4):e33807.
doi: 10.1371/journal.pone.0033807. Epub 2012 Apr 4.

Caffeine Ingestion Reverses the Circadian Rhythm Effects on Neuromuscular Performance in Highly Resistance-Trained Men

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Free PMC article
Randomized Controlled Trial

Caffeine Ingestion Reverses the Circadian Rhythm Effects on Neuromuscular Performance in Highly Resistance-Trained Men

Ricardo Mora-Rodríguez et al. PLoS One. .
Free PMC article

Abstract

Purpose: To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern.

Methods: Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg(-1); AM(CAFF) trial); ii) morning (10:00 a.m.) with placebo ingestion (AM(PLAC) trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PM(PLAC) trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s(-1) load). Isometric maximum voluntary contraction (MVC(LEG)) and isometric electrically evoked strength of the right knee (EVOK(LEG)) were measured to identify caffeine's action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST).

Results: In the PM(PLAC) trial, dynamic muscle strength and power output were significantly enhanced compared with AM(PLAC) treatment (3.0%-7.5%; p≤0.05). During AM(CAFF) trial, muscle strength and power output increased above AM(PLAC) levels (4.6%-5.7%; p≤0.05) except for BP velocity with 1 m s(-1) load (p = 0.06). During AM(CAFF), EVOK(LEG) and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AM(PLAC) trial (14.6% and 96.8% respectively; p≤0.05).

Conclusions: These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Experimental Protocol.
Twelve highly resistance-trained men, in a randomized, double-blind and placebo controlled experimental design, underwent a battery of neuromuscular and biochemical assessments under three different conditions; i) morning (10:00a.m.) with caffeine ingestion (i.e., 3 mg kg−1; AMCAFF trial); ii) morning (10:00a.m.) with placebo ingestion (AMPLAC trial); and iii) afternoon (18:00p.m.) with placebo ingestion (PMPLAC trial).
Figure 2
Figure 2. Effects of circadian rhythm pattern and caffeine ingestion on dynamic and isometric maximum strength and muscle power values for upper and lower body actions.
A) and B) Velocity for maximal power and; C) and D) Velocity for maximum strength loads for squat and bench press exercises; E) Maximal isometric voluntary contraction strength (MVCLEG) and electrically evoked strength (EVOKLEG) on the right knee; F) Maximal isometric grip strength. Trials were conducted in the morning (10:00 am) without (AMPLAC) or with caffeine ingestion (i.e., 3 mg kg−1; AMCAFF) and in the afternoon (18:00 pm; PMPLAC). Data are means ± SD. *Significant differences compared to the AMPLAC values. p≤0.05.
Figure 3
Figure 3. Catecholamine response to a maximal sympathetic stimulation bout of exercise.
Norepinephrine and Epinephrine changes following a bout of 6 free-weight squats repetitions with a load of 85% of 1 RM in the morning (10:00 am) without (AMPLAC) or with caffeine ingestion (i.e., 3 mg kg−1; AMCAFF) and in the afternoon (18:00 pm; PMPLAC). Data are means ± SD for 12 resistance-trained men. Plasma norepinephrine concentrations reflect whole body sympathetic nerve activation. *Significant differences compared to the PRE values of the same treatment. ‡Significant differences compared to the PRE AMPLAC values. †Significant differences compared to the POST AMPLAC values. p≤0.05.

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